Would this work on Nikon SB700?

Hello George, The FX-3 fits the Nikon SB-700. You can find it here: http://www.amazon.com/X-Tender-Better-Beamer-FX-3-Booster/dp/B000SLNNG4/ref=sr_1_1?s=photo&ie=UTF8&qid=1442238947&sr=1-1&keywords=FX-3Hope this helps.

is there a Better Beamer that fit the Metz m400?

I don't know if there is a better flash extender. The majority of the members in the Photo Club I belong to use the Better Beamer. Both price and function are the determining factors. We use the Better Beamer when we go photograph Hummingbirds in a canyon near Tucson. I suggest calling B & H or others that sell the Beamer to get the correct fit, that is what I had to do. Good Luck Doug

will this fit on a NW680 Neewer

Measure the height of your flash head or refer to the flash manual for exact measurements. Then compare the measurement with the dimensions below to determine the right size Better Beamer flash extender for your setup. FX-1: Nikon SB-24 and SB-28, Canon 430EZ and 199d, Minolta 5200 and 5400, Pentax 5000 AF, and Canon 380 will fit properly with shims included. Dimensions: 19⁄16″ (3.81 cm). For those 19⁄16″ in height, use the FX-1 Better Beamer. For those 19⁄16″, use the FX-2. The FX-1B includes shims to fit units slightly smaller than 19⁄16″. FX-1B: Nikon SB-80 and DB-80DX. NOTE: We do not recommend the use of the Better Beamer with the Nikon SB-50 due to problems with rigidity. Dimensions: 1½″ (3.81 cm) FX-2: Nikon SB-25 and SB-26, Canon 540EZ and 550EX, Sony HVL-F58AM, Sigma EF 500 & Minolta 5600HS (with shims - contact us for shims). Dimensions: 1¾″ (4.44 cm) narrow ear. FX-3: Custom-fitted for the Canon 580EX, 580EX II, 600 EX-RT and the Nikon SB-700 flash units. Dimensions: 1¾″ (4.44 cm) wide ear FX-4: Custom fitted to Nikon SB600 and SB800. Dimensions: 1½″ (3.81 cm) wide ear. FX-5: Custom fitted to Canon 430EX, Canon 430 EXIII. Dimensions: 1 9⁄16″ (3.96 cm) wide ear with added soft shim (contact us for shims). FX-6: Custom fitted to Nikon SB900 and Nikon SB-910. Also fits the newer Canon 600 EX IIRT (other Canon 600 flashes should use the FX-3). Dimensions: 1⅞″ (4.76 cm) wide ear. Hope this information is helpful! NatureScapes.net Store

Will this flashx tender fx4 fit on a nikon d810? also, will it flash for a 70-200mm and 200-400mm lens?

This unit is designed for an external flash unit. If your unit is one of the two listed, the answer is yes, it will attach to those units. Both the listed units will work on a several Nikon models. While the unit is intended for up to 300 mm lenses, depending upon the speed of thel lens, you might stretch its use to 400 mm.